It is commonly referred to as glass but it is actually a transparent ceramic. It is typically 3/16 thick. This highly transparent ceramic glass has virtually zero thermal expansion. It is produced in flat, rolled sheets. It is excellent for passing UV while blocking IR.

The Temperature Shock Resistance (TSR) of ceramic glass characterizes the ability of a panel to withstand the temperature shock in which cold water is poured onto a hot panel. As a result of the fact that the TSR of Pyroceram® is practically zero, the temperature shock caused by sudden cooling with cold water leads to only minor stresses. The shock resistance is therefore normally limited only by the maximum operation temperature: Short Term Usage: 760° C / 1,400° F. Long Term Usage: 680° C / 1, 256° F. These ceramic glasses have a Transparent-amber tint.

These products listed all have a crystalline component, like milk glass or Corningware. As with Corningware, the crystals that form within the glass have a negative CTE (they contract as they warm up, and expand as they cool down). The volume fraction of glass vs. crystals is adjusted until the overall CTE is zero (the glass expands exactly as much as the crystals contract). Usually these crystals are based on lithium compounds.

To make such a composite transparent, each individual crystal must be much smaller than the wavelength of light. The manufacturers almost achieve this: only the bluer wavelengths of visible light are short enough to be scattered by these very tiny crystals. Greens and reds pass through undisturbed, which is why we see an amber color.

CERAMIC GLASS - STOVE GLASS available in 3/16" and 1/8" inch thickness only. Only genuine ceramic glass can be used in High temperature applications of glass that is suitable for use in wood, pellet and coal burning stoves. It's thermal shock rating of 1380° F makes it ideal for any application where high temperature tolerance is required. Rarely used for fireplace doors. It often is used in industrial high temperature applications.

We currently stock this product, there is no visual or performance difference between pyroceram, neoceram, or robax, the difference is just trademarks, all 3 are transparent high temperature ceramic glass with a 1380° F thermal shock tolerance with a slight amber tint, slight texture, and available in 5mm (3/16) and 4mm (1/8) thickness. The glass that we supply is not ceramic coated or IR coated. It is ceramic all the way through allowing it be reversible.

Many homes in the United States and worldwide are heated by burning wood or Peat as a fuel source for heating homes. Many of these furnaces are constructed by case iron or heat treated steel. However, there is always a glass product that provides a view of the flame in the burning chamber. This is not ordinary glass product. Due to the extreme heat and pressure created inside the chamber, the glass needed has to withstand high heat conditions.

The glass product suited for this is a product call Pyroceram. There are also several names given for each product and each one creates different temperature tolerances. We carry the Pyroceram product.

Pyroceram is not ordinary glass. It is an amber transparent ceramic also known as Neoceram and other given names depending on the manufacturer. Pyroceram has entirely different characteristics from tempered glass. Pyroceram has a high thermal ceramic with a heat rating of around 1650 degrees and is normally used in high heat applications such as woodstoves and fireplace inserts. Fireplace doors do not generate enough heat to exceed the thermal rating so if you need to replace your fireplace door, high strength tempered glass is you best cost effective option. However, there are new fireplace door inserts. These new products are inserted into your fireplace and act as a mini wood stove. They do create enough heat for the use of Pyroceram. So, if you need to replace the glass in your fireplace swing doors, and not a fireplace insert or a woodstove, then you need a tempered product.

Pyroceram Ceramic glass breakage usually occurs as a result of impact or the retaining hardware was too tight or during eventual thermal breakdown which can take several years or even decades. When broken it will usually just crack like normal glass. Pyroceram is amber in color and is made of 3/16 thick glass and is the best glass product to replace for your wood stove.

The history of Pyroceram glass and scientific stuff...

In 1952, one of Corning's scientists, Dr. S. D. Stookey, made and accidental but important discovery when an oven malfunction overheated a piece of photosensitive glass on which he was working. The glass turned milky white as a result of heat-induced crystallization and did not break when dropped. The result was a ceramic-like material, the first in a new family of glass-ceramic materials that has led Corning into several new businesses.

This new Pyroceram® glass-ceramic material was extremely durable, corrosion resistant and had a very low coefficient of expansion. It was also transparent to radar, which made it ideal for use as nosecones on anti-aircraft missiles (Figure 1).

These space age characteristics allowed Pyroceram glass-ceramics to be very successfully adapted for commercial use as Corningware® products for cooking in 1959 (Figure 2). Pyroceram glass-ceramic's transparency to radar (microwaves) also allowed Corningware products to be used in microwave ovens, greatly extending their versatility in the kitchen.

Glass-ceramics next found a place in biology and chemistry laboratories when they were used in 1964 to make tops for Corning® hot plates and stirrers (Figure 3). Unlike metal tops, glass-ceramics are easy to clean, highly resistant to scratches, corrosion and chemical attack. Pyroceram tops heat up hotter than metal typically providing temperatures 200°C above metal top products. Pyroceram tops are also white allowing easy viewing of color contrasts in such applications as titrations. As a result, it has been the material of choice for Corning hot plates for over forty years.

In 1986, Dr. Stookey was awarded the National Medal of Technology for this and other material innovations, including photosensitive and photochromic glasses, he made while working for Corning.

Pyroceram is a material developed and trademarked by Corning Glass during the 1950s. Its development has been traced to Corning's work in developing photosensitive glass.[1] Corning credits S. Donald Stookey with its discovery; while conducting research on photosensitive glass, Stookey noted that an accidentally overheated fragment of the glass resisted breakage when dropped.[2]

The manufacture of the material involves controlled crystallization.[1] NASA classifies it as a Glass-ceramic product.[3]

After about 30 years of informal use as a standard in high heat (1000 degrees Celsius) applications, Pyroceram 9606 was approved as a certified reference material

Glass-ceramics are polycrystalline material produced through controlled crystallization of base glass. Glass-ceramic materials share many properties with both glasses and ceramics. Glass-ceramics have an amorphous phase and one or more crystalline phases and are produced by a so called "controlled crystallization" in contrast to a spontaneous crystallization, which is usually not wanted in glass manufacturing. Glass-ceramics have the fabrication advantage of glass as well as special properties of ceramics. Glass-ceramics usually have between 30% [m/m] to 90% [m/m] crystallinity and yield an array of materials with interesting properties like zero porosity, high strength, toughness, translucency or opacity, pigmentation, opalescence, low or even negative thermal expansion, high temperature stability, fluorescence, machinability, ferromagnetism, resorbability or high chemical durability, biocompatibility, bio-activity, ion conductivity, superconductivity, isolation capabilities, low dielectric constant and loss, high resistivity and break down voltage. These properties can be tailored by controlling the base glass composition and by controlled heat treatment/crystallization of base glass.

Glass-ceramics are mostly produced in two steps: First, a glass is formed by a glass manufacturing process. The glass is cooled down and is then reheated in a second step. In this heat treatment the glass partly crystallizes. In most cases nucleation agents are added to the base composition of the glass-ceramic. These nucleation agents aid and control the crystallization process. Because there is usually no pressing and sintering, glass-ceramics have, unlike sintered ceramics, no pores.

The commercially most important system is the Li2O x Al2O3 x nSiO2-System (LAS-System). The LAS-system mainly refers to a mix of lithium-, silicon-, and aluminum-oxides with additional components e.g., glass-phase forming agents such as Na2O, K2O and CaO and refining agents. As nucleation agents most commonly zirconium(IV)-oxide in combination with titanium(IV)-oxide is used. This important system was studied first and intensively by Hummel,[1] and Smoke.[2]

After crystallization the dominant crystal-phase in this type of glass-ceramic is a high-quartz solid solution (HQ s.s.). If the glass-ceramic is subjected to a more intense heat treatment, this HQ s.s. transforms into a keatite-solid solution (K s.s., sometimes wrongly named as beta-spodumene). This transition is non-reversible and reconstructive, which means bonds in the crystal-lattice are broken and new arranged. However, these two crystal phases show a very similar structure as Li could show.[3]

The most interesting properties of these glass-ceramics are their thermomechanical properties. Glass-ceramic from the LAS-System is a mechanically strong material and can sustain repeated and quick temperature changes up to 800–1000 °C. The dominant crystalline phase of the LAS-glass-ceramics, HQ s.s., has a strong negative coefficient of thermal expansion (CTE), keatite-solid solution as still a negative CTE but much higher than HQ s.s.. These negative CTE's of the crystal-phase contrasts with the positive CTE of the residual glass. Adjusting the proportion of these phases offers a wide range of possible CTE's in the finished composite. Mostly for today's applications a low or even zero CTE is desired. Also a negative CTE is possible, which means, in contrast to most materials when heated up, such a glass-ceramic contracts. At a certain point, generally between 60% [m/m] and 80% [m/m] crystallinity, the two coefficients balance such that the glass-ceramic as a whole has a thermal expansion coefficient that is very close to zero. Also, when an interface between material will be subject to thermal fatigue, glass-ceramics can be adjusted to match the coefficient of the material they will be bonded to.

Originally developed for use in the mirrors and mirror mounts of astronomical telescopes, LAS-glass-ceramics have become known and entered the domestic market through its use in glass-ceramic cooktops, as well as cookware and bakeware or as high performance reflectors for digital projectors.

The word "Pyroceram" is a generalized brand name that Corning used with respect to its glass-ceramic products. There is a belief that it specifically refers only to the Corning Ware formula, but this is incorrect. In company literature Centura is stated to be "Fashioned from remarkable Pyroceram brand glass ceramic ..." and there is no doubt that Centura has a different composition than Corning Ware.

Visions cookware was also called Pyroceram at times and the backstamps of Centura and Suprema restaurant ware also contain the word "Pyroceram". These products are not Corning Ware. So Pyroceram is just a brand name that encompasses the entire family of glass-ceramics rather than one specific formulation.

"Pyroceram" is a family of different glass-ceramics. Corning Ware and Centura are two types of Pyroceram. Image from 1963 leaflet.

The scientific field of glass-ceramics was first pioneered in the 1950s and quickly led to the introduction of Corning Ware in 1958. Corning Ware, Visions, Centura and Suprema are all glass-ceramics. This means they are materials that are glass in structure initially, but through heat treatment they become a ceramic.

An article like a casserole or saucepan is formed from melted glass, then it is re-heated and cooled under controlled conditions. The heat treatment makes crystals grow within the glass, turning it into a ceramic and dramatically improving the strength of the item.

The transformation from glass to ceramic is visible in the material's molecular structure. Glass has an amorphous structure, meaning that its atoms are certainly bound, but in irregular patterns. In contrast, the atoms of a ceramic are bound in very regular patterns, or crystals, i.e.: a crystalline structure.

Heat treatment is not the only requirement for encouraging crystals to grow. The glass must contain an ingredient that provides nucleation during heat treatment, i.e.: an atom that the crystal can grow around, or its nucleus. Titanium Dioxide serves this purpose in most glass-ceramic formulations.

Before heat treatment, Corning Ware is a transparent glass with an amber hue. Its appearance is very similar to amber Visions, but paler in color. After heat treatment, it is almost perfectly white and very densely opaque.

Opal Pyrex is also strengthened by crystallization, but it is not transformed sufficiently to be classified as a glass-ceramic. After the opal glass article is formed, it is re-heated in the annealing, or tempering, process by passing through a long oven known as a lehr and then cooled again.

The amount of crystal growth in opal glass measures 10% or even less, and overall it is still glass because its structure is predominantly amorphous. Materials in the glass-ceramics family can attain crystallization of 50% or more.

The substantial degree of crystallization in glass-ceramics translates to a huge gain in mechanical strength compared to ordinary annealed glass. The modulus of rupture of annealed glass ranges from 5000 to 10,000 psi, while this measurement for glass-ceramics is usually between 10,000 to 20,000 psi. Centura possesses even greater strength once it is glazed. The glaze acts as a compression layer, boosting its MoR to over 40,000 psi.

Glass-ceramics also differ greatly from traditional ceramics. Clay products are formed from a mix that is cold and wet, then air dried, usually at room temperature, and fired to gain the crystalline structure that provides strength. But the strength of traditional ceramics does not compare with the extraordinary durability of glass-ceramics.

The usual crystallization method for glass-ceramics creates an opaque product, and researchers were challenged with inventing a transparent version. Their first success came in 1966, but this clear colorless product did not reach the market due to a fear of hurting Pyrex and Corning Ware sales. There were also concerns that consumers would not be able to distinguish it from ordinary clear Pyrex. One proposed application for this glass-ceramic was a coffee percolator.

The progress made in this earlier project led directly to Visions stovetop ware, an amber-hued transparent glass-ceramic. The official name of Visions glass is Calexium and it was developed at Corning in France. The product line became available in France in the late 1970s, and it entered the North American market in 1983.

Sources:

Introduction to Manufacturing Processes, John A. Schey

The Generations of Corning, Davis Dyer and Daniel Gross.

"Method of Making Ceramics and Product Thereof", Stanley D. Stookey, United States Patent 2,920,971

"Profiles in Ceramics: S. Donald Stookey", The American Ceramic Society Bulletin, March 2000

"Profiles in Ceramics: George H. Beall" The American Ceramic Society Bulletin, June 2000